Neurotransmitter-specific synaptologies of vertebrate retinal neurons will be investigated in three program modules intended to describe retinal microcircuits with greater fidelity and provide an enhanced basis for comparing our knowledge of ectotherm visual processing with mammalian, especially human, visual performance. Module I: DOUBLE LABEL EXPERIMENTS (goldfish). Serial section electron microscope autoradiography of neurons selectively labeled by high affinity (3H) neurotransmitter uptake will be combined with: (A) Horseradish peroxidase histochemistry of ganglion cells filled by retrograde transport; (B) Gold-toning of Golgi-impregnated retinal neurons; or (C) Immunocytochemistry for putative peptide or conventional neurotransmitter containing neurons. These preparations will document the incidence of synaptic connections among GABAergic, glycinergic, serotoninergic, dopaminergic, putative taurinergic, putative peptidergic and morphologically characterized cells. The somatic and dendritic structures of neurochemically classified cells may be revealed by autoradiographic co-localization of (3H) neurotransmitter uptake in Golgi-impregnated cells. Module II: STRUCTURAL NEUROCHEMISTRY OF SALAMANDER RETINAS (mudpuppy and tiger salamander). Recognizing the continuing importance of urodele amphibians as physiological/pharmalogical models of visual processing, it has become critical to provide fundamental data on the types, distributions and connections of neurochemically defined retinal neurons. The urodele retina will be studied by serial section electron microscope autoradiography of (3H) GABA, glycine, taurine, serotonin and dopamine accumulating cells; immunocytochemistry will also be performed for some peptides, conventional neurotransmitters and their synthetic enzymes. Module III: EVALUATION OF CONVENTIONAL NEUROTRANSMITTERS IN AMACRINE AND BIPOLAR CELLS (goldfish, salamander, cat). Less thoroughly understood neurotransmitter systems (taurine, glycine, acetylcholine and acidic amino acids) will be evaluated through biochemical, autoradiographic, immunocytochemical or cytochemical means.